I haven't used one of the digital turntables, so take my observation as maybe being worth about as much as you have paid me for it. ;D
I guess you could pick the wrong one, or get a bad production model, but using the USB-digital turntable makes the process simple compared to all the gizmos and gadgets you might have to chain together otherwise. It also gets around the issue of whether you have an adequate sound card for the task.
The digital "stuff" that comes in via the USB is going to be raw digital audio which saved to a hard drive as is gets named .wav with out any processing being done to muddy anything up. Whether you save it in a .wav format long term becomes the question. You want to do your editing while it is still .wav..... things like chopping the silence off each end, taking out clicks, doing a bit of EQ if needed and and if appropriate, a bit of noise reduction. Only AFTER any such processing do you want to convert the audio to mp3 or whatever format will go into the Podcast.
If the Podcast is going to contain voice content I would prefer to put the voice and the audio from the vinyl into a finished podcast before I did any transfer to another format such as mp3 but from your description you could possibly have more material to store than you have space for. This will be easy for me to say: I'm spending YOUR money not mine.... but consider buying one of those external hard-drives that connects via USB for storage. I'm seeing 1-Terabyte units for something just north of $100 these days.
I would use the software for editing that you are most comfortable using. I have become an Audition "bigot" for that reason. You may have another software that is technically better, but using the one that let's you squeeze out the sound and editing style you want is the critical issue. Once you compress down to mp3 or other such Podcast format, whatever audio superiority one editing program has over another may be lost in the squeeze.
Not to be too much like a mother on this issue, but do keep in mind what kind of copyright issues you may need to satisfy.